We all use things to mark pages in our books: receipts, slips of paper, brochures, tickets, paper clips, and Post-it Notes. Post-it Notes have an adhesive on them which transfers to the surface it is applied to. This adhesive residue, in turn picks up dirt or other foreign particles and cause them to stick to the book. I understand the need to mark a pages or pages in books one might be using as research materials. I don’t want to be harsh or mean, but please remove Post-it Notes from books before you turn them in. It’s better for the books and their future users, and it is a considerate thing to do.